Regarding vehicles coupled to each other by using electrical couplers, a communication between the vehicles has been conventionally performed through an electric contact of the electrical coupler of each vehicle. Note here that in a condition where the vehicle is not coupled to another vehicle, an oxide film may be generated on a surface of the electrical coupler of each vehicle. When the vehicle is coupled to another vehicle under a condition that the oxide film is generated, a communication error in the communication between the vehicles is likely to be caused due to an influence of the oxide film.
As an example of a method for solving the above-mentioned problem, Patent Document 1 listed below discloses a technique that destroys an oxide film by applying a direct-current component to a contact portion of a connector. In a circuit in which a transmission amplifier is insulated by a transformer, the direct-current component is applied to the connector by connecting a direct-current voltage supply between the transformer and the connector.